In a human intervention study blood

In a human intervention study, blood GSH levels were evaluated over 6 wk in 18 male participants subjected to strenuous aerobic training and a dietary supplement of 1 g of WPI/kg of body mass per day. Blood GSH levels were significantly lower in those subjects who performed exercise that those who did not (P < 0.05). The addition of WP supplementation to an exercise regimen prevented this GSH depletion in blood (Middleton et al., 2004). In agreement, Sheikholeslami Vatani and Ahmadi Kani Golzar (2012) observed increased GSH plasma levels in 30 overweight young men who consumed WPI and performed resistance training for 8 wk (173 ± 22 nM GSH/L vs. control group, 144 ± 20 nM GSH/L; P < 0.05). Levels of GSH in plasma were also increased by 23% in steatohepatitis patients who received 20 g of WPI/d for 12 wk compared with GSH levels before WPI supplementation (Chitapanarux et al., 2009). In another human trial, 31 subjects received 15 to 45 g of pressurized WPI/d over a 2-wk period. The GSH levels in dihydroquercetin extracted from blood were 24% higher after 45 g of WPI consumption than participants who did not consume WPI (Zavorsky et al., 2007). In contrast, blood GSH levels remained unchanged over the 4-h sampling period in male subjects who received an acute dose of WPI (0.8–1.6 g of WPI/kg of BW) (Middleton et al., 2004). Measuring levels of GSH in plasma is one of the most common techniques to detect whey product antioxidant protection in vivo. A positive correlation exists between low plasma GSH levels and disorders in which oxidative stress is a contributing factor, such as cardiovascular disease (Shimizu et al., 2004), polycystic ovary syndrome (Murri et al., 2013), and autism (Frustaci et al., 2012). However, plasma GSH levels are unlikely to reflect intracellular GSH in target organs such as the liver, brain, or muscle routinely exposed to oxidative stress (Ballatori et al., 2009). In contrast, charting the oxidation levels of particular proteins involved in disease onset and progression would provide more relevant biomarkers in cellular assays and dietary intervention trials (Frijhoff et al., 2015).
CONCLUSIONS
ACKNOWLEDGMENTS
Introduction Human beings have evolved a sophisticated inner system to protect cells and organs against the free radical generated in vivo. However, an imbalance between the antioxidant protection system and free radicals could result in oxidative stress, which has been shown to be associated with various chronic disease such as rheumatoid arthritis, neurological degeneration, and even cancer [1]. The study of antioxidants has significantly increased recently. Although there is no conclusion regarding whether the intake of antioxidants could relief of oxidative stress, many food and pharmaceutical companies use antioxidants as a way to claim their have health benefits. Due to commercialization growth and research interest, there is a high demand to develop a reliable, quick and portable method for the quantitative determination of antioxidants in food, beverages, drugs and biological samples. Several analytical techniques have been developed for measuring the total or individual antioxidant capacity in different samples. For example, the antioxidant capacity method could be measured using chromatographic techniques [2–5]. However, chromatographic techniques require auxiliary extraction method with multiple separation processes since antioxidants commonly exist in foodstuffs. In contrast, the employment of electrochemical techniques for the determination of antioxidants has gained attention due to its rapid response, high sensitivity and ease of miniaturization. Direct electrochemical detection of antioxidants has been achieved in many electrodes such as glassy carbon electrode (GCE) [6] and platinum electrode [7]. However, this method always suffers high overpotential from the antioxidant molecules. Electrode surface modification has been applied for overcoming this problem. Many higher electrochemical performance materials were used for conventional electrode surface modification and consequently used for antioxidants sensing [8–10]. In comparison, enzyme and DNA modified electrodes have been applied for antioxidants sensing as well [11,12]. However, the surface modification of an electrode commonly suffers some drawbacks such as inactivation, non-renewability and high-cost.